It will be referred to, and if it expanded the family lands it will have more of an effect.
But surely you would never marry someone for political reasons. that would be horribly medieval. 
Yes. There will be dealings with the MC’s brother later on. In fact, depending on which way you take at the crossroads, you may wind up meeting him sooner rather than later.
@Rogar, @Zoilus, @Eiwynn
There are two major branches, of which at least one of them branches again almost straight away. There’ the path to become Archbishop, which will take place in Norwall and concern the MC mostly with the affairs of the reformist movement, cajoling for allies and power, establishing a rival church, that sort of thing. Then there’s the path to become an Exarch, and a path to attempt to become a Holy Father, both of which are bundled under the umbrella of staying with the Holy Mother Church. An Exarch will be returning to Norwall to get rid of the pesky reformists there and may wind up using a certain Earldom as a home base for that, while the Holy Father path will be more broader issues that revolve around re-establishing the Holy Father’s authority so the stray flocks can be brought back into the fold over a longer period of time.